This study evaluates the histological and biochemical changes that occurred in a semitendinosis autograft 4 years after intraarticular placement as an anterior cruciate ligament (ACL) substitute in a human patient. The graft was harvested during total knee replacement. Comparison to harvested ACL and hamstring tendon was made. Changes in collagen crimp pattern, cell type, glycosaminoglycan composition, and collagen crosslinking were present between the ACL autograft and the hamstring tendon. The appearance and biochemical properties of the semitendinosis autograft and the native ACL were similar 4 years following intraarticular placement. These observed phenomena could be attributed to functional adaptation, supporting the concept of ligamentization.